1. Field of the Invention
This invention relates to hypochlorite bleaching compositions, and more specifically to such compositions containing solubilized optical brighteners.
2. Description of the Relevant Art
A wide variety of aqueous compositions for improving the whiteness of fabrics or textiles, or the consumers' perception thereof, are known in the art. Chief among these are bleaching agents which improve fabric whiteness by oxidizing stains. Such bleaching agents include peroxygen, peracid, and halogen bleaches, the latter of which are most commonly used owing to their stability, effectiveness and low cost. Another wide-spread method of treating fabrics to increase the consumers' perception of fabric brightness is to deposit onto the fabric a fluorescent whitening agent, sometimes known as an optical brightener. Fluorescent whitening agents (FWAs) have the ability to absorb ultraviolet radiation and to re-emit it in the form of visible light, thus increasing the apparent brightness of the fabric treated therewith. It is especially advantageous to combine the fluorescent whitening agent with the bleach to achieve a fabric treatment composition which both removes stains to improve actual whiteness, and deposits FWAs to enhance apparent whiteness. There are, however, drawbacks associated with such compositions. Many FWAs are incompatible with halogen bleaches, as they will be oxidized thereby, destroying their effectiveness. Halogen-compatible FWAs are generally insoluble in aqueous solutions thereof, requiring additional components to either disperse, or solubilize them. Zimmerer et al. U.S. Pat. No. 3,939,153 represents a typical approach to formulating a FWA as a particulate dispersion. Such dispersions may be physically unstable, settling out over time, and even those that are relatively stable may result in undesirable brightener staining if the FWA does not uniformly dissolve in the wash liquor. Accordingly, it is most desirable to formulate halogen bleaches with a soluble FWA. This approach is represented by Payne et al U.S. Pat. No. 3,998,750 which utilizes a distyryl-type FWA, solubilized by alkaline earth cations. U.K. patent application No. 2,026,566 solubilizes a stilbene-type FWA using a fatty alkoxylated amine disulfide salt. EPA application 186,386, inventor Mansy, describes a stilbene-disulfonic acid (or salt) FWA solubilized by an amine oxide in a hypochlorite bleach. The formulation of Mansy requires a relatively high level of amine oxide and teaches a ratio of amine oxide to brightener of from 40:1 to 10:1. Mansy further teaches that the composition must be made up by dissolving surfactant and brightener in an aqueous solution, thereby forming a dilute aqueous base mixture of surfactant, FWA and water, an adding thereto sufficient hypochlorite to yield a volume of from 0.4 to 8 times the volume of the brightener/surfactant solution.
Applicants have surprisingly discovered however, that certain hereinafter defined FWAs can be stably solubilized in hypochlorite by low ratios of amine oxide:FWA. This is achieved by premixing FWA in concentrated surfactant, then adding directly to this concentrated premix an aqueous solution of the bleach, preferably hypochlorite, as well as any adjuncts. A pH adjusting agent aids the physical and chemical stability of the composition.
Accordingly, it is an object of the present invention to achieve a stable solution of fluorescent whitening agent and bleach.
It is another object of the present invention to provide a stable solution which minimizes brightener spotting on fabrics treated therewith.
It is another object of the present invention to provide a composition that is more cost effective, owing to the lower levels of expensive surfactant.
It is yet another object of the present invention to provide a concentrated brightener/surfactant premix which minimizes dilution of the halogen source, thus minimizing manufacturing costs and processing steps.